Lecture 15: Global Change and Resources

Back to the beginning with the Carbon cycle
Takes into account many of the things weÕve learned
	rock cycle
	sedimentary processes
	atmospheric processes
	etc

Draw Carbon Cycle
	lithosphere -- ls, oil & gas
	atmosphere -- greenhouse -- trees and animals
	anthropogenic contribution
[use WestbrookÕs residence time chart to illustrate cycling time -- geo time]

Greenhouse Warming -- CO2 in the Atmosphere
	does not let Earth radiation escape
	[BroekerÕs Earth radiation diagram]
	H2O is a greenhouse as well.
	Why is it so hot at night in Florida?
	-- Because of the humidity -- H2O is a greenhouse gas, does not let air temp cool off.

In order to understand the future, we need to know past climate history.
Timing of the ice ages.
How do we know when ice ages occurred in the past?
	-By looking at Oxygen isotopic composition of seafloor sediments.

16O is lighter than 18O

-review mass number = protons plus neutrons
isotope = member of an element (defined by number of protons) with different number of
neutrons
isotopes behave similarly (or predictably) during chemical reactions

During evaporation, more 16O evaporates into atmosphere than 18O, because of less mass.
ice is 3.5% richer in 16O than seawater.
This makes oceans richer in 18O, or 18/16O ratio increases (by about 0.2%)
This ratio is recorded in ocean-floor sediments.
So by dating sea-floor sediments and measuring their isotopic composition, we can interpret past
climate history.

What happens during glaciation?
	water goes from ocean to polar ice caps (less water in ocean)
	therefore 18/16O ratio in oceans increases (less 16O)
	Consequently, 18/16O ratio increases in sea-floor sediments as well.
	--Note that fig 19.10 shows ice and fresh water sediments, which show the opposite affect
as sea water sediments.

What does historical ice-age pattern look like?
	-approx. 100k-year cycle.
	Glacial max was approx 18,000 years ago.
	Come out of ice ages very quickly.

[BroeckerÕs 100k -timescale history]

Why this regular periodicity?

The Milkovitch Theory.
Aspects of EarthÕs orbit around the sun
1) EarthÕs spin axis is tilted -- this produces the seasons -- one orbit around sun / year
2) EarthÕs orbit is eliptical -- not always the same distance away from sun.
3) EarthÕs orbit experiences ŌtugsĶ from other planets, especially Jupiter
	this affects both orbit and tilt

All of these interact, both re-enforcing and counter-acting each other.
Combined affects make an approx 100k-year cycle
It is thought that increased seasonality is what causes glaciation -- especially summers
cooler summers does not melt all ice
hotter summers do melt more ice
warmer winters still produce precipitation that forms polar ice caps.

This theory was challanged by Richard Miller, who lectured here recently.
He favored a periodic plunge through a meteor or dust belt, to reduce solar radiation.

We are now in an interglacial
[BroeckerÕs Ōinduced interglacial]
For the past million years or so, the Earth has mostly been colder than now.
Florida Indian ruins are buried offshore.

In older periods of Earth history, however, the Earth has been much hotter.
This is studied through distributions of Marine organisms and isotopic composition.
CO2 follows temperature -- or visa verse -- that is the big question.
Cretaceous and parts of Tertiary were much warmer
One idea is different ocean circulation patterns
Another idea (not mutually exclusive) is that huge plume-head eruptions released lots of CO2
from the deep Earth to make hotter temperature [fig B19.2].
The Cretaceous was a time of many LIPS (Large Igneous Provinces).


General Circulation Models try to model climate by taking into account all effects
They are difficult because cloud formation and ocean circulation are poorly understood.
biogeochemistry -- i.e., Gaia -- is also poorly understood.
grid size is about 500 km.

CO2 follows temperature
[ice core graph; 19.4, 19.6]
Historical increase in temperature is much more rapid than would be expected in a geological
system.
That is the big difference. We are coming out of a glacial period, very fast

Effects of increased temperatures

Rise of Sea Level due mostly to the thermal expansion -- not melting polar ice caps
	Ice caps like ice cubes, when they melt, the glass does not suddenly overflow.
-Especially worrisome to island nations, who have become the staunchest supporters of
international treaties to reduce CO2 emmisions.
Melting glaciers would certainly contribute to this effect.
-What would happen to Downtown Santa Cruz?

Upset Ecosystems --many changes in vegetation patterns, thawing of frozen ground
-- disturb agriculture

Increased Storminess(?) increased precipitation and big storms.

Melting of Gas Hydrates(?) (frozen gas molecules buried in marine sediments)
-- These would escape to atmosphere, contribute to greenhouse effect -- feedback.

Back to Carbon Cycle

Carbon in lithosphere (geologic cycle) keeps Earth cool
Limestone and hydrocarbons are carbon sinks.
Keeps Carbon out of atmosphere and in the ground.

Role of Tectonics
What if no tectonics?
Some CO2 comes out through mantle-derived volcanism
If no tectonics, no way to return CO2 to mantle.
If no CO2 contribution from the mantle, then Earth becomes too cold,
white albedo kicks in.
Geology, with the help of biology (Gaia) help make Earth comfortable.

Hydrocarbons as an Earth Reasource

Q: How long does it take for hydrocarbons to form?
A: A long time -- on a geologic time scale.

This part of class gets very social

King HubbertÕs prediction on hydrocarbon use.
Bell-shaped curve
We are on the down side for Lower 48 oil and gas,
just as he predicted
-perhaps one of the most accurate economic and social predictions of the last quarter century.
This story is changed somewhat when Middle East oil is taken into consideration.
[figure from Miller]
Given instability in that region, difficult to understand why U.S. is not doing everything it can to
promote alternative sources of Energy.

Story can be broadenned to other resources
U.S. depends on South Africa for many mineral resources.
Makes it easy to understand our acceptance of apartied for so many years.
[Chart from enviro geology]